In a polymer electrolyte fuel cell, a cell is formed as a minimum unit by sandwiching a membrane electrode assembly (MEA), which is composed of a fuel electrode and an air electrode sandwiching an electrolyte membrane formed of a polymer electrolyte membrane, with two separators, and a plurality of cells are stacked to form a fuel cell stack, which can provide high output.
The mechanism for electric power generation employed by the polymer electrolyte fuel cell is well known, and in a nutshell, fuel gas, such as hydrogen-containing gas, is supplied to the fuel electrode (i.e., anode-side electrode), and oxidant gas, such as a gas mainly containing oxygen and air, is supplied to the air electrode (i.e., a cathode-side electrode). The hydrogen-containing gas is supplied to the anode-side electrode through a fuel gas flow passage, and is dissociated into electrons and hydrogen ions by the action of a catalyst of the electrode. The electrons move to the cathode-side electrode through an external circuit. Meanwhile, the hydrogen ions pass through the electrolyte membrane and reach the cathode-side electrode, where the hydrogen ions bond to oxygen and the electrons passing through the external circuit, to thereby produce reaction water. The heat generated by the bonding reaction of hydrogen with oxygen and electrons is recovered by means of cooling water. Further, water generated in the cathode-side electrode (which will hereinafter be referred to as “generated water”) is drained from the cathode side.
Both of the anode-side electrode and the cathode-side electrode of the fuel cell are formed of catalyst layers, and these catalyst layers include stacks of gas diffusion layers for diffusing hydrogen-containing gas and oxidant gas, respectively. If the drainage of the generated water generated by the above-described reaction is interrupted in the flow passage on the cathode side, a clogging phenomenon (“flooding phenomenon”) may occur in the cathode-side electrode. More specifically, if the drainage of the generated water is interrupted in the cathode-side flow passage, the cathode-side flow passage is narrowed by the generated water. This may increase the passage resistance in the cathode-side flow passage, and thus may cause reduction of electric power generation output.
The below-described Patent Document 1 discloses that, with the aim of overcoming the interruption of gas diffusibility and the deterioration of drainage, a flow passage forming member which forms a flow passage for passing supplied gas therethrough is formed of a plurality of communication segments, and that the further the segments are located on the supplied gas downstream side, the narrower the flow passage widths of the segments become.